The present invention relates to a power plant with a blow-off device which permits rapid pressure reduction in a pressure vessel or combustion chamber with hot gas. It is particularly intended for a PFBC plant in which fuel is burnt in a fluidized bed of particulate material at a pressure considerably exceeding the atmospheric pressure. "PFBC" is formed of the initial letters in the English expression Pressurized Fluidized Bed Combustion. In such a plant a bed vessel and a cleaning plant are arranged within a pressure vessel. Combustion gases generated in the bed vessel drive a turbine. The turbine drives a compressor which delivers compressed combustion air to the pressure vessel.
In the event of an operational disturbance causing a gas turbine trip, the energy supply must be quickly interrupted to prevent the turbine from racing. By closing the valve in the hot gas conduit from the bed vessel and in the air conduit to the pressure vessel, the turbine and the compressor are isolated from the bed vessel and the pressure vessel, respectively. At the same time a valve in a by-pass conduit between the compressor and the turbine is opened.
U.S. patent application No. 007,226 U.S. Pat. No. 4,744,212 describes one way of slowly reducing the pressure in a combustion chamber and a pressure vessel in the case of a permanent disturbance.
However, in the case of a serious operational disturbance, it is desirable to have the possibility of rapidly achieving a blow-off of the hot gases in the plant. The high gas temperature, up to about 950.degree. C., causes the blow-off valve to be subjected to great temperature stresses which damage the valves and result in the valves not being tight after closing after a blow-off. U.S. Pat. No. 4,498,285 to Kreij shows a valve arrangement for rapid blow-off of hot combustion gases in which combustion gas from a bed vessel is mixed with air from a surrounding pressure vessel with compressed combustion air upstream of a blow-off valve in the pressure vessel wall or in a blow-off conduit from the pressure vessel. Despite the temperature reduction ahead of the blow-off valve, the temperature stresses are considerable. Simultaneous opening of two valves, one from the combustion chamber and one from the pressure vessel, involves certain problems.